This invention relates to an air compressor of the type having a piston which reciprocates back and forth in a cylinder. The piston sucks air into the cylinder as it moves through an intake stroke and then pressurizes the air as it moves reversely through a compression stroke. In a conventional compressor, the piston is reciprocated by means of a crank or eccentric associated with a power-rotated shaft and coupled to the piston by a connecting rod.
During initial movement of the piston through its compression stroke, torque of only relatively low magnitude need be applied to the shaft in order to move the piston since the air in the cylinder offers little resistance to such movement. As the air compresses, however, greater torque is required to move the piston and overcome the resistance of the pressurized air.